The present invention relates generally to electron acceptors (or withdrawing groups) which can be used in the preparation of polymeric thin films for waveguide media, and specifically to dicyanomethylendihydrofuran-based electron acceptors, and methods of making the same.
Thin films of organic or polymeric materials with large second order nonlinearities in combination with silicon-based electronic circuitry can be used in systems for laser modulation and deflection, information control in optical circuitry, as well as in numerous other waveguide applications. In addition, novel processes through third order nonlinearity such as degenerate four-wave nixing, whereby real-time processing of optical fields occurs, have utility in such diverse fields as optical communications and integrated circuit fabrication. The utility of organic materials with large second order and third order nonlinearities for very high frequency application contrasts with the bandwidth limitations of conventional inorganic electrooptic materials currently in use.
Numerous optically responsive monomers and polymers have been developed for use in organic materials which, in turn, can be used in the waveguide applications described above. For example, U.S. Pat. No. 5,044,725, which is incorporated herein by reference in its entirety, describes numerous polymer compositions which provide suitable nonlinear optical response. U.S. Pat. No. 5,044,725 describes, for example, a preferred polymer composition comprising an organic structure containing an electron donating group and an electron withdrawing group at opposing termini of a bridge. To achieve nonlinear optic (NLO) stability, however, thermally stable electron acceptors must be obtained.
Most recently, U.S. Pat. No. 6,067,186 (the ""186 patent), disclosed a class of organic chromophores which can result in hardened electro-optic polymers suitable for electro-optic modulators and other devices such as optical switch.
The synthesis of thermally stable electron accepting (or withdrawing) groups for organic nonlinear optical applications are generally known in the art. Although many different electron acceptors have been reported in the literature, few, if any, have showed both suitable thermal stability and very high electron acceptance at the same time. Accordingly, electron acceptors which exhibit both thermal stability and very high electron acceptance are desired.
The present invention is directed to compounds which can serve as electron acceptors in, for example, thin films for waveguides. Preferred compounds of the invention have Formula (I): 
where R1 and R2 are base stable moieties. R1 can be substituted and unsubstituted C1-C10 alkyl, R2 can be substituted and unsubstituted C2-C10 alkyl, and R1 and R2 each, independently, can be substituted and unsubstituted C4-C10 alkenyl, substituted and unsubstituted C4-C10 alkynyl, substituted and unsubstituted aryl, substituted and unsubstituted alkylaryl, substituted and unsubstituted carbocycles, substituted and unsubstituted heterocycles, substituted and unsubstituted cyclohexyl, or (CH2)nxe2x80x94Oxe2x80x94(CH2)n where n is 1-10; provided there is no methylene between the * carbon and an sp2 or sp hybridized carbon. Alternatively, R1 and R2 together form a ring structure or a substituted ring structure. R3 is either substituted and unsubstituted C1-C5 alkyl, substituted and unsubstituted C1-C5 alkenyl, substituted and unsubstituted C1-C5 alkynyl. As contemplated herein, the term xe2x80x9calkylarylxe2x80x9d does not include benzyl.
The present invention is also directed to a method of preparing compounds having Formula I comprising the steps 1) providing an alkylvinylether, 2) contacting the alkylvinylether with a strong base to form a first intermediate compound, 3) contacting the first intermediate compound with a ketone to form a second intermediate compound, and 4) reacting the second intermediate compound with dicyanomethane in the presence of a metal alkoxide base, or other appropriate base known to those skilled in the art, to form a compound having Formula I.
As used herein, the phrase xe2x80x9celectron acceptorxe2x80x9d is used synonymously with xe2x80x9celectron accepting groupxe2x80x9d and xe2x80x9celectron withdrawing groupxe2x80x9d, and refers to electronegative organic compounds or substituents which attract electron density from the pi-electron system when the conjugated electron structure is polarized by the input of electromagnetic energy.
The present invention relates, in part, to novel electron acceptors which have utility in organic nonlinear optical applications and methods of preparing the same. The compounds of the invention function as electron acceptors (or as electron withdrawing groups) which exhibit both thermal stability and very high electron acceptance simultaneously. The compounds of the invention can be used in, for example, polymeric organic materials for optical waveguides. Such polymeric organic materials are described in, for example, U.S. Pat. Nos. 5,044,725, 4,795,664, 5,247,042, 5,196,509, 4,810,338, 4,936,645, 4,767,169, 5,326,661, 5,187,234, 5,170,461, 5,133,037, 5,106,211, and 5,006,285, each of which is incorporated herein by reference in its entirety.
In preferred embodiments of the invention, the electron acceptor compounds are dicyanomethylenedihydrofuran-based compounds comprising Formula I: 
where, R1 can be substituted and unsubstituted C1-C10 alkyl, R2 can be substituted and unsubstituted C2-C10 alkyl, and R1 and R2 each, independently, can be selected from the group consisting of substituted and unsubstituted C2-C10 alkyl, substituted and unsubstituted C4-C10 alkenyl, substituted and unsubstituted C4-C10 alkynyl, substituted and unsubstituted aryl, substituted and unsubstituted alkylaryl, substituted and unsubstituted carbocycles, substituted and unsubstituted heterocycles, substituted and unsubstituted cyclohexyl, and (CH2)nxe2x80x94Oxe2x80x94(CH2)n where n is 1-10; provided there is no methylene between the * carbon and an sp2 or sp hybridized carbon.
The substituted alkyl, alkenyl, alkynyl, carbocyclic, and heterocyclic groups can comprise one or a plurality of substituents including, for example, fluorine, chlorine, D, and the like. In addition, the heterocyclic groups can comprise O, N, S, and the like.
The aryl groups preferably include, but are not limited to, phenyl, fluorenyl, and naphthyl. The aryl groups, carbocycles, heterocycles, and cyclohexyl can also be substituted by one or a plurality of substituents including, for example, D, halides, including fluorine, chlorine and bromine. The alkylaryl groups preferably comprise C1-C10 alkyl and the substituted alkylaryl groups comprise the substitutions for the alkyl and aryl groups described above.
In more preferred embodiments of the invention, R1 and R2 each, independently, are selected from the group consisting of, carbocycle, heterocycle, cyclohexyl, phenyl, cycloalkyl, cycloalkenyl, and substituted phenyl. Additional moieties for R1 and/or R2, independently, include, but are not limited to the following: 
and the like.
In even more preferred embodiments of the invention, R1 is CH3 and R2 is a substituted phenyl. Preferably, the substituted phenyl is selected from the group consisting of, but not limited to: 
and the like.
Alternatively, R1 and R2 together form a ring structure or a substituted ring structure from 3 to 7 atoms total with 5 or 6 atoms being preferred. Preferably, the ring structure is substituted or unsubstituted carbocycle, substituted or unsubstituted heterocycle, or substituted or unsubstituted cyclohexyl. The substituted ring structure can comprise substituents including, but not limited to, halides, including fluorine, chlorine and bromine. A preferred compound having a ring structure formed by R1 and R2 comprises 
R3 is preferably selected from the group consisting of substituted and unsubstituted C1-C4 alkyl, substituted and unsubstituted C1-C4 alkenyl, substituted and unsubstituted C1-C4 alkynyl. More preferably, R3 is C3 alkenyl (-CH=CH-CH3), C5 alkenyl (xe2x80x94CHxe2x95x90CHxe2x80x94CHxe2x95x90CHxe2x80x94CH3), C2 alkynyl (xe2x80x94Cxe2x89xa1CH), or C4 alkynyl (xe2x80x94xe2x89xa1Cxe2x80x94Cxe2x89xa1CH). Most preferably, R3 is CH3. The substituted alkyl, alkenyl, and alkynyl groups can comprise one or a plurality of substituents including, for example, F, D, or Cl.
In preferred embodiments of the invention, R3 is selected from the group consisting of C1-C4 alkyl, C1-C4 alkenyl, and C1-C4 alkynyl. In more preferred embodiments of the invention, R3 is CH3.
The present invention is also directed to methods of preparing electron acceptors of the invention. In a particularly preferred embodiment of the compound of Formula I, R3 is CH3, and the product can be prepared by the following steps depicted in Scheme I: a) providing an alkylvinylether, b) contacting the alkylvinylether with a strong base to form a first intermediate compound, c) contacting the first intermediate compound with a ketone to form a second intermediate compound, and d) reacting the second intermediate compound with dicyanomethane in the presence of a second base to form a compound having Formula I. 
Compounds having an R3 moiety other than CH3 can be prepared by substituting the appropriate starting compound as is well known to persons skilled in the art. Each of the above mentioned steps is described in greater detail below.
In preferred embodiments of the invention, an alkylvinylether in a solvent is the starting material. The solvent is, preferably, tetrahydrofuran (THF), 1,4-dioxane, or the like. Although the alkylvinylether depicted in Scheme I is ethylvinylether, other alkylvinylethers can be used. The alkylvinylether preferably comprises the formula CH3xe2x80x94(CH2)xxe2x80x94Oxe2x80x94CHxe2x95x90CHR4, where x is 1-3 and R4 is H or C1-C4 alkyl. Most preferably, the alkylvinylether is methylvinylether or ethylvinylether.
The alkylvinylether is contacted with a strong base to form a first intermediate compound. Preferably, the strong base has a pKa greater than the ethylinic C-H bond xcex1 to the oxygen function of the alkylvinylether. For example, see Advanced Organic Chemistry, Third Ed., Jerry March, 1985, Table 1, pp. 220-222. In preferred embodiments of the invention, the strong base is an alkyl lithium, or an alkali metal salt of an alkyl anion, including, but not limited to, t-BuLi or sec-BuLi. The alkylvinylether is preferably contacted with the strong base between about xe2x88x9270xc2x0 C. and xe2x88x9285xc2x0 C., most preferably at about xe2x88x9278xc2x0 C.
The first intermediate compound is contacted with a ketone and then an acid/alcohol/water solution to form a second intermediate compound. Numerous acid/alcohol/water solutions known to those skilled in the art can be used in the present invention. The acid/alcohol/water solution is preferably HCl/MeOH/H2O, HBr/EtOH/H2O, or H2SO4/EtOH/H2O. Preferably, the contacting is at room temperature. Preferably, the pH is adjusted between 1 and 4.
Preferably, the ketone comprises the formula 
wherein R1 can be substituted and unsubstituted C1-C10 alkyl, R2 can be substituted and unsubstituted C2-C10 alkyl, and R1 and R2 each, independently, can be selected from the group consisting of, substituted and unsubstituted C1-C10 alkyl, substituted and unsubstituted C1-C10 alkenyl, substituted and unsubstituted C1-C10 alkynyl, substituted and unsubstituted aryl, substituted and unsubstituted alkylaryl, substituted and unsubstituted carbocycles, substituted and unsubstituted heterocycles, substituted and unsubstituted cyclohexyl, and (CH2)nxe2x80x94Oxe2x80x94(CH2)n where n is 1-10. Alternatively, R1 and R2 together form a ring structure or a substituted ring structure, as described above.
Preferably, the Cxe2x95x90C and Cxe2x89xa1C bonds of the alkenyl and alkynyl groups are not immediately adjacent the carbonyl group of the ketone compound.
The substituted alkyl, alkenyl, and alkynyl groups can comprise one or a plurality of substituents including, for example, fluorine, D, and chlorine.
The aryl groups preferably include, but are not limited to, fluorenyl, phenyl, and naphthyl. The aryl groups, carbocycle groups, heterocycle groups, and cyclohexyl can also be substituted by, for example, D, halides, including fluorine and chlorine. Preferably, the alkylaryl groups comprise C1-C10 alkyl and the substituted alkylaryl groups can comprise the substituents for the alkyl and aryl groups described above.
In more preferred embodiments of the invention, R1 and R2 each, independently, are selected from the group consisting of, cyclohexyl, phenyl, and substituted phenyl.
In even more preferred embodiments of the invention, R1 is CH3 and R2 is a substituted phenyl. Preferably, the substituted phenyl is selected from the following: 
Alternatively, R1 and R2 together form a ring structure or a substituted ring structure or a heterocyclic ring structure. Preferably, the ring structure is substituted or unsubstituted 5 or 6 member rings, including, but not limited to, 5 or 6 member heterocyclic rings and fluorenyl. The substituted ring structure can comprise substituents including, but not limited to, halides, including fluorine, chlorine and D.
The second intermediate compound is reacted with dicyanomethane in the presence of a second base at the appropriate temperature to form a compound having Formula I. The second base is preferably a metal alkoxide including, but not limited to, NaOC2H5, NaOH, KOH, and K2CO3. After contacting the second intermediate compound with dicyanomethane in the presence of a second base, dilute acid such as, for example, HCl, is added for neutralization of the resultant electron acceptor compound.